UN probe of Syria chemical attack site stalls after gunmen fire on inspection team

The devastated town of Douma was the scene of a chemical attack

A UN team visiting the site of a suspected chemical weapons attack in Syria have come under fire, delaying a fact-finding mission to the area and heightening fears that crucial evidence could be tampered with.

The team visiting Douma retreated to their base in Damascus after unidentified gunmen shot at them, according to Ahmet Uzumcu, the head of the international chemical weapons watchdog.

Inspectors from the Organization for the Prohibition of Chemical Weapons have been waiting since Saturday to visit Douma, the site of the alleged April 7 attack.

They were blocked by the Syrian government and its ally, Russia, on Monday, which control Douma, and on Tuesday the advance security team from the UN came under fire.

A Syrian security employee was slightly wounded in the crossfire on Tuesday, the Russian military said, but no Russian servicemen were at the site of the attack.

The US Defense Secretary warned the Syrian regime would likely use the delay to destroy evidence Credit: AP

Uzumcu did not say when the experts would next deploy. The UN meanwhile has said more security measures are needed before the inspectors can go in.

In the US, Defense Secretary Jim Mattis warned the Syrian regime would likely use the delay to destroy evidence of any involvement in the attack.

"We are very much aware of the delay that the regime imposed on that delegation," Mattis said.

"But we are also very much aware of how they have operated in the past ... In other words, using the pause after a strike like that to try to clean up the evidence before the investigation team gets in."

Russia has accused the rebels of staging the attack with support from Britain, an allegation that Britain has strongly denied.

Russia's military has insisted it has uncovered a chemical weapons stockpile left behind by the rebels in Douma, but the claim could not be independently verified.